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Lecture 2

Lecture 2 Jan 9 2014.docx

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PSYC 3100
Pat Barclay

Evolutionary Psychology 3100 Lecture Two: Natural Selection: Genes and Behaviour January 9 2014  Part A: Evolution by Natural Selection  All current species having evolved from common ancestors  Humans are right in the middle of the primate lineage  When comparing humans and chimps: humans did not evolve from chimps, we evolved from a common ancestor with the chimp  Common ancestor = some characteristics of chimps, some human, some monkey, etc.  This should point out there is no ladder of progress -> but rather everyone is equally evolve  Chimps are not failed humans, they are simply really good at being chimps  Evolution  Definition: Change in gene frequency in populations  Genes influence various traits, change in inherited traits in populations  Four Mechanisms for Population Frequency Change :  Natural Selection : some individuals being more likely to reproduce than others, and therefore their traits are more likely to be passed on • A) Competition: not enough resources for all individuals as they reproduce -> struggle for existence and reproduction with limited resources and mates • B) Heritable Variation: individuals differ, more similar to their parents on average • C) Differential Reproduction: some individuals reproducing more than others, you need it to depend on the variation • “Natural selection is a non-random difference in reproductive output among replicating entities, often due indirectly to difference in survival in a particular environment, leading to an increase in the proportion of beneficial, heritable, characteristics within a population from one generation to the next” –Gregory 2009 Article (courselink)  Mutation: random, genes can mutate into alternate versions of the original trait, selection is not random, variation is required and thus is a means to variation  Migration: some individuals leave a population, some enter a new population, and thus reflects a change in the population  Genetic drift: change in frequency that is random with respect to the effect of the genes • Random fluxuations in the proportion of each kind of gene in the population -> it’s a statistical ‘fluke” • A) It’s a random statistical deviation from average (Example: eye colour, Father and mother both carry brown and blue eye traits -> four possible outcomes, but one gene combination make occur more frequently) • B) Random effects: Example: all blue-eyed people die off (meteor kills them, no fault of their own); this is a random effect and changes the proportionate genes in the population. Going to 2/3 chance for brown eyes.  Overall Evolution -> is a combination of these four factors  What evolves?  Must increase reproductive success -> must have a statistical effect on the likeliness of the person reproducing and surviving, not psychological benefit (ex. Fear, sex, relationships) -> we evolved to enjoy things that are statistical associated with reproductive success  Any trait has to maximize the benefit to cost ratio -> many traits carry both a benefit and a cost. (ex. Fear in the face of predators or foraging in a forest in open to predator -> rabbit in a field feeding -> benefit= food, cost= predator
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